This application is based upon and claims the benefit of priority of Japanese Patent Applications No. H.11-94246 filed on Mar. 31, 1999 and No. H. 12-16202 filed on Jan. 25, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a stator manufacturing method, in particular, a method for forming in a twisted shape a near letter U shaped wire or near letter U shaped double wires.
2. Description of Related Art
A stator of a large-scale starter to be installed in automobiles employs an electromagnetic coil having a large cross sectional area for flowing large electric current.
To manufacture the electromagnetic coil, at first, a wire made of conductive material such as copper is formed in a near letter U shaped wire 10. Next, a turning portion 12 of the near letter U shaped wire 10 is twisted so that a twisted wire 1 may be formed (refer to FIG. 7).
The twisted wires 1 are press fitted for assembly into slots of a yoke and, after assembly to the yoke, both ends thereof are further deformed and connected with each other by welding and so on to complete the electromagnetic coil.
A twisting formation apparatus 100 for mass-producing the twisted wire 1 is provided with, as shown in FIG. 10, an outside holding ring 45 and an inside holding ring 35 into which a pair of straight line portions 11, 11 of the near letter U shaped wire 10 are separately inserted and held respectively and which are arranged concentrically, and further provided with an inside jig 3 and an outside jig 4 which are relatively rotatable.
According to this conventional twisting formation apparatus 100, a twisting formation of the near letter U shaped wire 10 is conducted in such a manner that the respective straight line portions 11, 11 of a plurality of the near letter U shaped wires are inserted into the inside and outside holding rings 35 and 45, upper ends of all of the turning portions 12 are initially aligned or fixed by a retaining element 101, and, then, the turning portions 12 are twisted by a relative rotating movement of the inside and outside jigs 3 and 4.
However, in the twisting formation apparatus 100 mentioned above, when the retaining element 101 is operative for initial alignment of the upper ends of the turning portions, a gap A comes out in height direction since a pull is given to the turning portion 12 by a deformation of the near letter U shaped wire 10. On the other hand, when the retaining element fixes the upper end of the turning portion 12, the straight line portions 11,11 are moved upward as the turning portion is pulled up during the formation of the near letter U shaped wire 10. Thus, there exists a state that the near letter U shaped wire 10 is not supported in an up and down direction or is fixed by one point during the deformation process, resulting in a problem that the twisted shape formation of the turning portion is not likely to be uniform.
The present invention has been made in view of the above mentioned problem, and an object of the present invention is to provide a twisting formation apparatus in which a plurality of the near letter U shaped twisted wires or near letter U shaped twisted double wires are formed in a uniform shape at a time.
The twisting formation apparatus enables to form at a time in a uniform twisted shape a plurality of the near letter U shaped wires, in such a manner that at least either the turning portion or respective leading ends of the straight line portions are urged toward the straight line portions by biasing means.
Therefore, not only the twisted wires may be formed in a uniform shape, but also a generator or a motor such as a starter necessitating a large amount of the near letter U shaped wires may be manufactured with a minimum cost. In the apparatus, plural kinds of near letter U shaped double wires piled up with each other may be formed in a uniform twisted form.
According to the stator manufacturing apparatus for wires in pile, while the biasing means urges the turning portion of the wire arranged most outside, the first and second supporting portions support the respective leading ends of pair of straight line portions of the wire arranged most outside at predetermined positions in respective axial directions of pair of straight line portions.
Thus, each of pair of straight line portions is prevented from being relatively moved in an axial direction of each of the straight line portions from the first or second holding jig.
Further, the near letter U shaped wires partly project out of the first and second holding jigs. The respective wires projecting on the turning portion side have lengths to .an extent that, when the first and second holding jigs are relatively moved, only the respective projecting turning portions are deformed and, thus, the respective straight line portions held in the first and second holding jigs are not drawn out toward the turning portions.
Therefore, the first and second supporting portions serve to prevent damages of the near letter U shaped wires due to frictions between the respective straight line portions and the respective holding jigs.
The near letter U shaped wires in pile are respectively provided with the turning portions having different curvature radiuses. Therefore, a starting portion where the wire arranged inside (inside wire) is deformed is more far away from a center of the turning portion than a starting portion where the wire arranged outside (outside wire) is deformed. As a result, after the twisting formation process, a height length of the inside wire becomes shorter than that of the outside wire.
Therefore, as another aspect of the present invention, the stator manufacturing apparatus is provided with the second biasing mechanism for urging the leading ends of the straight line portions of the inside wire. Thus, when the turning portion of the inside wire is twisted, an upper surface of the turning portion of the inside wire is maintained to press against a lower surface of the turning portion of the outside wire, even if the length of the inside wire becomes shorter.
As a result, a twisted shape fluctuation of the turning portion (turning portion 63) of the inside wire may be prevented, as the inside wire is twisted also at a state that a movement in an axial direction thereof is restricted.
As a further aspect of the present invention, the stator manufacturing apparatus is provided with the third biasing mechanism for urging respective leading ends of the straight line portions of the outside wire toward respective directions of the straight line portions, after the turning portions of the plural kinds of near letter U shaped wires arranged in piles have been twisted.
As a result, the respective leading end positions of the outside wire are accurately aligned by the third biasing mechanism for deforming the outside wire, even if the respective leading end positions are fluctuated to some extent during the previous process, so as to absorb such a fluctuation.
As a furthermore aspect of the present invention, the first holding portion is formed in a ring shape and the second holding portion is also formed in a ring shape on an outer circumference side of and concentrically with the first holding portion. Therefore, a relative rotating movement of the first and second holding jigs cause to twist the turning portions of the near letter U shaped wire or double wires. The twisted wires formed as above mentioned are, then, inserted into slots of a stator core. The insertion into the slots becomes easy because the stator core is formed generally in a ring shape.
Another object of the present invention is to provide manufacturing methods as processes executed by the stator manufacturing apparatus mentioned above.